The present invention is directed to a permeable base transistor for applications in the microwave field.
A permeable base transistor, for example, is described in the article by R. A. Murphy and J. D. Murphy, "Performance and Producibility of the GaAs Permeable Base Transistor" in Microwave Journal, July 1987, pages 101 through 116, incorporated herein. In such a permeable base transistor, a grid-shaped base of tungsten is embedded in a collector layer of GaAs. This collector layer is limited by high-impedance GaAs material to the side of the base grid in order to limit the flow of current from a surface-wide emitter layer onto the area occupied by the base grid. When a potential is applied, the flow of current through the collector is controlled by the grid. Technological processes for the manufacture of such transistors are described in the publication by M. A. Hollis et al, "Advances in the Technology for the Permeable Base Transistor," in SPIE, Vol. 797, pages 335 through 347, incorporated herein. Another overview article is that of C. O. Bozler, "Current Prospects for the Permeable Base Transistor," in surface Science 174, 487-500 (1986), incorporated herein.
In vertical channel field effect transistors, the vertical flow of current in the semiconductor material is controlled by metal gates laterally applied around the channel at both sides. Care must thereby be exercised to see that no electrical contacts exist between the semiconductor material and the metal electrodes of the gate.